In a case of an electric vehicle (referred to also as EV) which runs only by an electric motor serving as a driving source, the electric motor has a flat torque characteristics. Accordingly, in general, a power train has a configuration arranged to output by a combination between the electric motor of the driving source, and a speed reduction device having a constant transmission gear ratio.
In the thus-constructed electric vehicle, there is a large problem to ensure a cruising range (driving range). First, an increase of a battery capacity and a weight reduction of the vehicle are conceivable as a method for increasing the cruising range. However, in a case where the battery capacity is increased, the weight of the vehicle is increased. Therefore, the cruising range may be decreased.
Moreover, the decrease of the consumed power by decreasing the size of the electric motor of the driving source is conceivable as the method for increasing the cruising range in the electric vehicle. However, in this case, it cause the deficiency of the output of the electric motor. For preventing the deficiency of the output, it is necessary to combine with a speed reduction device having a higher transmission gear ratio, or to combine with a transmission having variable transmission gear ratio. In a case of the former, the vehicle runs at a characteristic value at which the motor efficiency is wrong in the vehicle high speed region. In a case of the latter, it is possible to avoid this by varying the transmission gear ratio.
A patent document 1 discloses a configuration in which the electric motor outputs by a combination with a stepped transmission, as an example in which the transmission is applied to the electric vehicle. However, in this case, the gear stage is needed to be the multi stages for efficiently driving the small electric motor in the wide speed region. Accordingly, the switching of the gear stages becomes frequent. The number of the shift shock generated at the each switching of the gear stage is increased. The riding feeling is deteriorated.
On the other hand, a continuously variable transmission (CVT) with an auxiliary transmission mechanism in which the auxiliary transmission mechanism is combined in a belt type continuously variable transmission (variator) is effective as a mechanism which can efficiently drive the small electric motor in the wide speed range, and which can suppress the frequency of the shift shock. Besides, a patent document 2 discloses a configuration which is not an electric vehicle, and which is arranged to output by a combination of an internal combustion engine and the CVT with the auxiliary transmission mechanism.
It is conceivable that the CVT with the auxiliary transmission mechanism of the patent document 2 is applied to the electric vehicle. However, the variator of the CVT needs applying the large axial thrust for clamping to sandwich the belt between the pulleys. The auxiliary transmission mechanism needs the switching operation of the gear stages. The patent document 2 does not describes these concrete methods. If the generally used hydraulic methods are used, the oil pump of the high output for satisfying these is needed.
For driving the oil pump of the high output, the motor for driving the pump which has a suitable output is needed. An SOC (a state of charge) of the battery is decreased by the power consumed by this motor for driving the pump. Accordingly, a cruising range of the electric vehicle is decreased. Moreover, the oil pump and the motor for driving the pump causes the cost-up and the increase of the weight of the vehicle. Accordingly, these decrease the cruising range of the electric vehicle.
Moreover, in the case of the CVT, in general, the power transmitting efficiency at the high speed and the high load is not good, and the electric power consumption at the high speed running is not good, relative to an automatic transmission using a gear mechanism using a planetary gear and so on.
This deterioration of the electric power consumption causes the decrease of the cruising range of the electric vehicle. In consideration of these points, the development of the art is desired.